1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of the Related Art
Various semiconductor devices are conventionally known. One of the known semiconductor devices is an IPM (Intelligent Power Module). A semiconductor device of this type includes a plurality of semiconductor elements, a lead including a plurality of island portions, a heat dissipation member and a sealing resin. The semiconductor elements are mounted on the island portions, respectively. The island portions are bonded to the heat dissipation member. The sealing resin covers the semiconductor elements, the island portions and the heat dissipation member. The semiconductor elements are electrically connected to each other appropriately via wires, so are the semiconductor elements and the lead. An example of the IPM is disclosed in JP-A-2011-243839.
In a semiconductor device configured as an IPM, the semiconductor element heats up during use. Due to the heat, the lead, the heat dissipation member and the sealing resin are thermally expanded. Generally, the lead, the heat dissipation member and the sealing resin are made of different materials. Thus, thermal stress is generated at the portions where these members are bonded to each other. When e.g. the lead and the sealing resin partially separate from each other due to thermal stress, proper insulation may not be provided between the semiconductor elements or between the semiconductor elements and the lead.
Since the heat dissipation member is provided for dissipating the heat generated at the semiconductor element to the outside, part of the heat dissipation member is exposed from the sealing resin. Thus, the edge of the interface between the heat dissipation member and the sealing resin is exposed to the outside. Depending on use environment of the semiconductor device, moisture and so on may enter the interface. When moisture enters deep into the device, the heat dissipation member and the sealing resin may separate from each other, which may lead to corrosion of e.g. the semiconductor element.
In a semiconductor device configured as IPM, thermal stress is applied also on the wires bonded to the semiconductor elements or the lead. Since each wire has a relatively discontinuous shape at the bonding portion, stress tends to be intensively applied on the bonding portion. Due to such intensive stress application, the wire may be detached from the semiconductor element or the lead.
Thermal stress is applied also on the portion where the semiconductor element and the island portion are bonded to each other. The semiconductor element is bonded to the island portion with a bonding material such as solder or Ag paste. When the bonding strength of the semiconductor element and the island portion with the bonding material is insufficient, the semiconductor element may be detached from the island portion.
Generally, the lead is made of a metal. Thus, the portion where the lead and the sealing resin are bonded together is the portion where different materials, i.e., metal and resin are bonded together. Since the coefficient of thermal expansion is considerably different between metal and resin, thermal stress is likely to occur. When the lead and the sealing resin become detached from each other due to thermal stress, proper insulation cannot be provided.